1. Field of the Invention
This invention relates to amorphous metal magnetic components; and more particularly, to a generally three-dimensional bulk amorphous metal magnetic component for large electronic devices such as magnetic resonance imaging systems, television and video systems, and electron and ion beam systems.
2. Description of the Prior Art
Although amorphous metals offer superior magnetic performance when compared to non-oriented electrical steels, they have long been considered unsuitable for use in bulk magnetic components such as the tiles of poleface magnets for magnetic resonance imaging systems (MRI) due to certain physical properties of amorphous metal and the corresponding fabricating limitations. For example, amorphous metals are thinner and harder than non-oriented silicon-steel and consequently cause fabrication tools and dies to wear more rapidly. The resulting increase in the tooling and manufacturing costs makes fabricating bulk amorphous metal magnetic components using such techniques commercially impractical. The thinness of amorphous metals also translates into an increased number of laminations in the assembled components, further increasing the total cost of the amorphous metal magnetic component.
Amorphous metal is typically supplied in a thin continuous ribbon having a uniform ribbon width. However, amorphous metal is a very hard material making it very difficult to cut or form easily, and once annealed to achieve peak magnetic properties, becomes very brittle. This makes it difficult and expensive to use conventional approaches to construct a bulk amorphous metal magnetic component. The brittleness of amorphous metal may also cause concern for the durability of the bulk magnetic component in an application such as an MRI system.
Another problem with bulk amorphous metal magnetic components is that the magnetic permeability of amorphous metal material is reduced when it is subjected to physical stresses. This reduced permeability may be considerable depending upon the intensity of the stresses on the amorphous metal material. As a bulk amorphous metal magnetic component is subjected to stresses, the efficiency at which the core directs or focuses magnetic flux is reduced resulting in higher magnetic losses, increased heat production, and reduced power. This stress sensitivity, due to the magnetostrictive nature of the amorphous metal, may be caused by stresses resulting from magnetic forces during operation of the device, mechanical stresses resulting from mechanical clamping or otherwise fixing the bulk amorphous metal magnetic components in place, or internal stresses caused by the thermal expansion and/or expansion due to magnetic saturation of the amorphous metal material.
The present invention provides a low-loss bulk amorphous metal magnetic component having the shape of a polyhedron and being comprised of a plurality of layers of amorphous metal strips. Also provided by the present invention is a method for making a bulk amorphous metal magnetic component. The magnetic component is operable at frequencies ranging from about 50 Hz to 20,000 Hz and exhibits improved performance characteristics when compared to silicon-steel magnetic components operated over the same frequency range. More specifically, a magnetic component constructed in accordance with the present invention and excited at an excitation frequency xe2x80x9cfxe2x80x9d to a peak induction level xe2x80x9cBmaxxe2x80x9d will have a core loss at room temperature less than xe2x80x9cLxe2x80x9d wherein L is given by the formula L=0.0074 f (Bmax)1.3+0.000282 f1.5 (Bmax)2.4, the core loss, the excitation frequency and the peak induction level being measured in watts per kilogram, hertz, and teslas, respectively. Preferably, the magnetic component will have (i) a core-loss of less than or approximately equal to 1 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 60 Hz and at a flux density of approximately 1.4 Tesla (T); (ii) a core-loss of less than or approximately equal to 12 watts-per-kilogram of amorphous metal material when operated at a frequency of approximately 1000 Hz and at a flux density of approximately 1.0 T, or (iii) a core-loss of less than or approximately equal to 70 watt-per-kilogram of amorphous metal material when operated at a frequency of approximately 20,000 Hz and at a flux density of approximately 0.30 T.
In a first embodiment of the present invention, a bulk amorphous metal magnetic component comprises a plurality of substantially similarly shaped layers of amorphous metal strips laminated together to form a polyhedrally shaped part.
The present invention also provides a method of constructing a bulk amorphous metal magnetic component. In a first embodiment of the method, amorphous metal strip material is cut to form a plurality of cut strips having a predetermined length. The cut strips are stacked to form a bar of stacked amorphous metal strip material and annealed to enhance the magnetic properties of the material and, optionally, to transform the initially glassy structure to a nanocrystalline structure. The annealed, stacked bar is impregnated with an epoxy resin and cured. The preferred amorphous metal material has a composition defined essentially by the formula Fe80B11Si9.
In a second embodiment of the method, amorphous metal strip material is wound about a mandrel to form a generally rectangular core having generally radiused corners. The generally rectangular core is then annealed to enhance the magnetic properties of the material and, optionally, to transform the initially glassy structure to a nanocrystalline structure. The core is then impregnated with epoxy resin and cured. The short sides of the rectangular core are then cut to form two magnetic components having a predetermined three-dimensional geometry that is the approximate size and shape of said short sides of said generally rectangular core. The radiused corners are removed from the long sides of said generally rectangular core and the long sides of said generally rectangular core are cut to form a plurality of polyhedrally shaped magnetic components having the predetermined three-dimensional geometry. The preferred amorphous metal material has a composition defined essentially by the formula Fe80B11Si9.
The present invention is also directed to a bulk amorphous metal component constructed in accordance with the above-described methods.
Bulk amorphous metal magnetic components constructed in accordance with the present invention are especially suited for amorphous metal tiles for poleface magnets in high performance MRI systems; television and video systems; and electron and ion beam systems. The advantages afforded by the present invention include simplified manufacturing, reduced manufacturing time, reduced stresses (e.g., magnetostrictive) encountered during construction of bulk amorphous metal components, and optimized performance of the finished amorphous metal magnetic component.